Translational instrumentation for spondylolisthesis and scoliosis reduction

ABSTRACT

An instrument includes a distraction mechanism having a proximal end and an opposed distal end. The distal end includes opposed first and second end members. A first vertebral endplate spreader includes a proximal spreader section mounted to the first end member of the distraction mechanism. The first spreader also includes a distal spreader section operatively connected to the proximal spreader section for lateral movement relative to the proximal spreader section. A second vertebral endplate spreader is mounted to the second end member of the distraction mechanism. The distraction mechanism is configured and adapted to distract the spreaders apart and to retract the spreaders together along a distraction axis. The distal spreader section of the first spreader is configured to move relative to the second spreader in a lateral direction relative to the distraction axis for correction of vertebral alignment, as in treatment of spondylolisthesis, scoliosis, and the like.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/237,385, filed on Dec. 31, 2018, which is a divisional of U.S. patentapplication Ser. No. 15/362,165, filed on Nov. 28, 2016 (U.S. Pat. No.10,166,048), which is a continuation in part of U.S. patent applicationSer. No. 14/569,218, filed Dec. 12, 2014. U.S. patent application Ser.No. 14/569,218, filed Dec. 12, 2014, is a divisional application of U.S.patent application Ser. No. 13/287,811, filed on Nov. 2, 2011 (U.S. Pat.No. 8,936,599). The contents of each above referenced application areincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to instruments and methods of treatingspinal conditions, and more particularly to instruments and methods fortreating spondylolisthesis, scoliosis, and the like.

2. Description of Related Art

Spondylolisthesis is a spinal disorder that arises from two separateconditions. The first involves a lytic defect in the parsinterarticularis, otherwise known as a spondylolysis. The lyticcondition most commonly occurs where the lumbar spine meets the sacrum,e.g., at L5-S 1. The second condition involves a slippage of thevertebra related to degenerated disc disease and facet arthrosis. Thedegenerative condition usually involves L4-5 segments. However,spondylolisthesis can occur at any level in the lumbar and less commonlyin the cervical spine. Treatment of spondylolisthesis often involves afusion of the two vertebra involved. Motion sparing technologies, suchas total disc replacements, are also used to treat milder cases ofdegenerative spondylolisthesis.

Spondylolisthesis treatment options routinely include spinal fusionprocedures. These can be performed with a combined anterior andposterior approach. The anterior approach is performed via a directanterior transperitoneal or retroperitoneal approach or lateralapproach. This surgery allows direct removal of the majority of thedisc, and placement of structural grafts in the disc space. Graftmaterials include autogenous bone from the iliac crest, allograft, andbone morphogenic protein. The discectomy procedure allows a mobility ofthe motion segment and enhances fusion rates. This is because anteriorgrafts are placed under compression as compared to posterior fusionmasses, which are under tension. The broad surface area between theendplates allow for higher fusion rates.

The distraction of the collapsed disc space of the listhetic segmentallows a mild reduction of the listhesis. This reduction is enhanced byimpacting a lordotically shaped graft within the intervertebral space.Alternatively, motion sparing technologies have been used for thisproblem. Posterior reduction techniques using pedicle screw and rodsystems have a significant risk of nerve root traction injuries. None ofthe traditional instruments, including instruments used in anteriorapproaches, allow for a combination of both distraction of the discspace and correction of listhesis.

Such conventional methods and systems have generally been consideredsatisfactory for their intended purpose. However, there is still a needin the art for instrumentation to allow for a combination of distractionof the disc space and correction of the listhesis. There also remains aneed in the art for such instrumentation that can be used from anteriorand other approaches. The present invention provides a solution forthese problems.

SUMMARY OF THE INVENTION

The subject invention is directed to a new and useful instrument forspinal procedures, such as for treating spondylolisthesis, scoliosis,and the like. The instrument includes a distraction mechanism having aproximal end and an opposed distal end. The distal end includes opposedfirst and second end members. A first vertebral endplate spreaderincludes a proximal spreader section mounted to the first end member ofthe distraction mechanism. The first spreader also includes a distalspreader section operatively connected to the proximal spreader sectionfor lateral movement relative to the proximal spreader section. Thedistal spreader section is configured and adapted to engage a vertebra.

A second vertebral endplate spreader is mounted to the second end memberof the distraction mechanism. The second spreader is configured andadapted to engage a vertebra. The distraction mechanism is configuredand adapted to distract the spreaders apart and to retract the spreaderstogether along a distraction axis responsive to action imparted on theproximal end of the distraction mechanism. The distal spreader sectionof the first spreader is configured to move relative to the secondspreader in a lateral direction relative to the distraction axis forcorrection of vertebral alignment.

In certain embodiments, a pair of guides is provided engaged with theproximal and distal spreader sections to maintain a parallelrelationship between the proximal and distal spreader sections duringrelative lateral travel of the proximal and distal spreader sections.The guides can be mounted to the distal spreader section and can beslideably engaged to the proximal spreader section.

The instrument can include a linear actuator engaged with the proximaland distal spreader sections to actuate relative lateral travel of theproximal and distal spreader sections. The linear actuator can include athreaded screw engaged to threads in the proximal spreader section. Thethreaded screw can be rotatably engaged with the distal spreader sectionso rotation of the threaded screw adjusts separation of the proximal anddistal spreader sections for relative lateral travel thereof.

In another aspect, at least one of the proximal and distal spreadersections can include a bone screw passage for accommodating a bone screwto engage the distal spreader section to a vertebra. It is alsocontemplated that the distal spreader section of the first spreader andthe second spreader each include at least one tong for engaging opposedvertebral endplates for distraction of opposed vertebrae.

The invention also provides a method of correcting vertebral alignment.The method includes engaging a distal spreader section of a firstvertebral endplate spreader to a first vertebra and engaging a secondvertebral endplate spreader to a second vertebra proximate to the firstvertebra. The method includes a step of distracting the first and secondspreaders apart along a distraction axis to distract the first andsecond vertebrae from one another. The method also includes translatingthe distal spreader section of the first spreader relative to the secondspreader laterally relative to the distraction axis for correction ofalignment of the first and second vertebrae.

The steps of engaging the first and second spreaders to the vertebraecan include approaching the vertebrae with the spreaders from ananterior approach. From such an anterior approach, the step oftranslating can include moving the superior of the two vertebrae in aposterior direction to correct a listhesis condition of the vertebrae.It is also contemplated that the step of translating can include movingthe superior of the two vertebrae in an anterior direction to correct aretrolisthesis condition of the vertebrae.

The steps of engaging the first and second spreaders to the vertebraecan include approaching the vertebrae with the spreaders from a lateralapproach. From a lateral approach, the step of translating can includemoving the two vertebrae relative to one another in a lateral directionto correct a lateral slippage condition of the vertebrae related toscoliosis. These and other features of the systems and methods of thesubject invention will become more readily apparent to those skilled inthe art from the following detailed description of the preferredembodiments taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject inventionappertains will readily understand how to make and use the devices andmethods of the subject invention without undue experimentation,preferred embodiments thereof will be described in detail herein belowwith reference to certain figures, wherein:

FIG. 1 is a side elevation view of an exemplary embodiment of aninstrument constructed in accordance with the present invention, showingthe vertebral endplate spreaders mounted to the distal end of a handoperable mechanism for manipulating the spreaders between distracted andretracted positions, and also showing the driver tool for actuatinglateral movement of the distal sections of the upper and lowerspreaders;

FIG. 2 is a plan view of the instrument of FIG. 1 without the driver,showing the engagement of the spreaders to the hand operable mechanism;

FIG. 3 is an exploded perspective view of the spreaders and driver ofFIG. 1, showing the tongs for engaging upper and lower vertebrae;

FIG. 4 is an exploded perspective view of the upper and lower spreadersof FIG. 3, showing the separate proximal and distal sections of the eachspreader as viewed from above;

FIG. 5 is a side elevation view of the instrument of FIG. 1, showing theinstrument being introduced from an anterior approach to a listheticpair of lumbar vertebrae;

FIG. 6 is a side elevation view of the instrument of FIG. 1, showing thetongs of the instrument being positioned between the listheticvertebrae;

FIG. 7 is a side elevation view of the instrument of FIG. 1, showing theupper and lower spreaders of the instrument mounted to the respectivevertebrae;

FIG. 8 is a side elevation view of the instrument of FIG. 1, showing theupper and lower spreaders of the instrument distracting the listheticvertebrae;

FIG. 9 is a side elevation view of the instrument of FIG. 1, showing theupper and lower spreaders laterally translated relative to one anotherfor correction of the listhesis.

FIG. 10 is a perspective view of another exemplary embodiment of aninstrument constructed in accordance with the present invention, showinga vertebral endplate spreader with a belt mounted to the distal end of adriver tool;

FIG. 11 is an exploded perspective of the instrument of FIG. 10, showingthe teeth of the belt;

FIG. 12 is a perspective view of another embodiment of an instrumentconstructed in accordance with the present invention, showing a geartransmission;

FIG. 13 is a perspective view of the instrument of FIG. 10, showing theinstrument being introduced from a lateral approach to a listhetic pairof lumbar vertebrae and the vertebral endplate spreader being positionedbetween the listhetic pair of vertebrae;

FIG. 14 is a side elevation view of a portion of the instrument of FIG.10, showing the position of the vertebral endplate spreader between thelisthetic vertebrae;

FIG. 15 is a side elevation view of the instrument of FIG. 10, showingthe position of the vertebral endplate spreader between the listheticvertebrae as the sprocket is rotated counter clock-wise;

FIG. 16 is a side elevation view of the instrument of FIG. 10, showingthe position of the vertebral endplate spreader between the vertebrae ina corrected position;

FIG. 17 is a side elevation view of the instrument of FIG. 10, showingthe placement of an implant between the corrected vertebrae;

FIG. 18 is a perspective view of the instrument of FIG. 10, showing theremoval of the vertebral endplate spreader and the placement of anotherimplant;

FIG. 19 is a perspective view of another exemplary embodiment of aninstrument constructed in accordance with the present invention, showinga vertebral endplate spreader with a belt mounted to the distal end of adriver tool;

FIG. 20 is an exploded perspective of a portion of the instrument ofFIG. 19, showing the worm gear interface between the driver handle andthe drive sprocket;

FIG. 21 is a perspective view of the instrument of FIG. 19, showing theinstrument being introduced from anterior approach to a listhetic pairof lumbar vertebrae;

FIG. 22 is a perspective view of the instrument of FIG. 19, showing thevertebral endplate spreader positioned between the vertebrae aftercorrection of the listhesis and showing an implant between thevertebrae;

FIG. 23 is a side elevation view of the instrument of FIG. 19, showingthe removal of the vertebral endplate spreader and the placement ofanother implant; and

FIG. 24 is a schematic depiction of a kit for performing spinaldistraction and vertebral alignment constructed in accordance with anembodiment of the present invention, showing a plurality of driverhandles, vertebral spreaders, implants and bendable screws.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectinvention. For purposes of explanation and illustration, and notlimitation, a partial view of an exemplary embodiment of an instrumentin accordance with the invention is shown in FIG. 1 and is designatedgenerally by reference character 100. Other embodiments of instrumentsin accordance with the invention, or aspects thereof, are provided inFIGS. 2-24, as will be described. The system of the invention can beused to treat spondylolisthesis, scoliosis, and the like.

Instrument 100 includes a distraction mechanism 102 having a proximalend 104 and an opposed distal end 106. Distal end 106 includes opposedfirst and second end members 108 and 110, respectively. A firstvertebral endplate spreader 112 includes a proximal spreader section114. Proximal spreader section 114 is mounted to first end member 108 ofdistraction mechanism 102 by mounting pin 122 shown in FIG. 2. Firstspreader 112 also includes a distal spreader section 116 operativelyconnected to proximal spreader section 114 for lateral movement relativeto proximal spreader section 114. A second vertebral endplate spreader118 is mounted to second end member 110 of distraction mechanism 102 bymounting pin 124, which is identified in FIG. 1. The first and secondspreaders 112 and 118 are each configured to engage a respectivevertebra for correction of vertebral alignment as will be described ingreater detail below.

Distraction mechanism 102 is configured and adapted to distract thespreaders 112 and 118 apart from one another and to retract thespreaders 112 and 118 together along a distraction axis A responsive toaction imparted on proximal end 104 of distraction mechanism 102. Forexample, if a user squeezes the handles of proximal end 104, spreaders112 and 118 will be distracted apart from one another, and if a userallows the handles of proximal end 104 to move apart, for example byaction of spring 120, spreaders 112 and 118 will be retracted towardsone another.

Referring now to FIG. 3, in addition to being able to move together andapart along distraction axis A, spreaders 112 and 118 can also movelaterally with respect to one another, i.e., in a lateral directionrelative to distraction axis A. This lateral movement is made possibleby the fact that the spreaders 112 and 118 are each split into proximaland distal sections 114 and 116 to vary the offset as needed by thepreexisting listhesis. Driver 126 is used to turn actuator screws 128 toactuate the displacement of distal spreader sections 116 relative toproximal spreader sections 114.

Lateral actuation of spreaders 112 and 118 is further described withreference to FIG. 4, which shows parts of spreaders 112 and 118separated and in the orientation of the procedures described below withreference to FIGS. 5-9. A pair of guides 130 is provided for eachspreader 112 and 118, engaged with the proximal and distal spreadersections 114 and 116 to maintain a parallel relationship between theproximal and distal spreader sections 114 and 116 during relativelateral travel thereof. Guides 130 are rigidly mounted in bores 132 ofdistal spreader sections 116 and are slideably engaged in bores 134 ofproximal spreader sections 114.

A linear actuator is provided in each spreader 112 and 118 in the formof actuator screw 128, the threads of which engage with correspondingthreads in bore 138 of the respective proximal spreader section 114.Each actuator screw 128 is rotatably engaged to a respective distalspreader section 116, with actuator pins 140 mounted in bores 142 andengaged with groove 144 of each respective actuator screw 128. Rotationof actuator screw 128 adjusts separation of the proximal and distalspreader sections 114 and 116 for relative lateral travel thereof.

Each distal spreader section 116 includes two bone screw bores 146 toprovide passages for bone screws to affix each distal spreader section112 to a respective vertebra. Proximal spreader sections 114 includesbone screw grooves 148 to provide passage for bone screws and anysuitable driver device for affixing distal spreader sections 112 torespective vertebra. Each of the distal spreader sections 116 includes apair of tongs 150 for engaging opposed vertebral endplates fordistraction of opposed vertebrae, as described in greater detail below.

Referring now to FIGS. 5-9, exemplary methods are described of usinginstrument 100 for correction of vertebral alignment. FIG. 5schematically shows instrument 100 approaching listhetic vertebrae L4and L5 from an anterior approach. The upper or first spreader 112 hasits distal spreader section 116 with corresponding tongs 150 in aretracted position. The lower or second spreader 118 has its distalspreader section 116 and corresponding tongs in an advanced position.The relative positions of the upper and lower distal spreader sections116 corresponds to the offset in alignment of the L4 and L5 vertebrae.As indicated in FIG. 6, tongs 150 of distal spreader section 116 offirst spreader 112 are engaged to the listhetic endplate of the L4vertebra, i.e., the superior or cephalad of the two listhetic vertebrae,and prongs 150 of second spreader 118 are engaged to the adjacentendplate of the L5 vertebra, i.e., the inferior or caudal vertebra.

With instrument 100 engaged with the listhetic vertebrae as shown inFIG. 6, the vertebrae can be distracted apart as shown in FIGS. 8 and 9.FIG. 7 shows bone screws affixing the first and second spreaders 112 and118 to the respective vertebrae prior to distraction. Those skilled inthe art will readily appreciate that one or both spreaders 112 and 118can be affixed with bone screws before or after distraction withoutdeparting from the spirit and scope of the invention. Moreover, bonescrew affixation may be omitted for one or both of the spreaders 112 and118, for example if the forces engaging the respective prongs 150 to thevertebrae provide sufficient fixation without bone screws. Having bothspreaders 112 and 118 secured with screws to the respective vertebraeprovides extra stability.

With the spreaders 112 and 118 affixed to the respective vertebrae asshown in FIG. 7, the proximal end 104 of distraction mechanism 102 canbe actuated to distract the vertebrae along distraction axis A asindicated by the heavy arrows in FIG. 8. With the listhetic vertebrae L4and L5 distracted, a corpectomy, discectomy, or the like can beperformed as needed.

Referring now to FIG. 9, direct posterior translational force is appliedafter a thorough discectomy and distraction has been performed. In orderto correct the listhesis, driver 126 is engaged with actuator screw 128up upper spreader 112 and turned to spread the upper proximal and distalspreader sections 114 and 116 apart. The actuator screw 128 on lowerspreader 118 can also be turned to move the lower distal spreadersection 116 in the opposite direction. This action translates the distalspreader sections 116 relative to the proximal spreader sections 114laterally with respect to distraction axis A for correction of alignmentof the L4 and L5 vertebrae. The action of driver 126 and distal spreadersections 116 are indicted by the heavy arrows of FIG. 9. Universal joint152 accommodates a range of angles of approach for driver 126 for easeof application. Driver 126 is depicted with a female hex head, whichthose skilled in the art will readily appreciate is exemplary, as anysuitable driver/head type or linear actuator type can be used withoutdeparting from the spirit and scope of the invention.

During an operation as described above, the surgeon can decide whether acomplete or partial reduction of the listhesis should be attempted.After adequate reduction has been achieved, an interbody graft or motionsparing device can be placed through the enhanced slot between thesuperior and inferior distractor tongs 150. The surgeon can check bydirect visualization or intra-operative x-rays as to the vertebralalignment and placement of the interbody graft(s) or motion sparingdevice. If a fusion is performed, instrument 100 is then removed,including the anterior screws. Supplemental anterior plate fixation canthen be applied using the holes previously made in the vertebrae toaffix the spreaders 112 and 118. The bores 134 in spreader 112 andcorresponding bores 134 in spreader 118 are spaced apart to allow for acorresponding anterior plating system after the reduction has beenperformed.

Instrument 100 will thus allow a correction of vertebral alignmentrelated to spondylolisthesis. The systems and methods described hereincan also be applied for a retrolisthesis, which is a much less commonspinal condition. In this case, the lateral motion of distal spreadersections 116 is reversed to be anterior rather than posterior.Furthermore, it is also contemplated that a smaller version ofinstrument 100 can be used for other applications where smaller size isneeded, for example in use on the cervical spine.

In the orientation shown in FIGS. 5-9, first spreader 112 may bereferred to as the upper, superior, or cephalad spreader, and secondspreader 118 may be referred to as the lower, inferior, or caudalspreader. Those skilled in the art will readily appreciate that whileeach of the spreaders 112 and 118 is shown and described as split intoproximal and distal sections 116 and 114 for lateral movement, it isalso possible to use only one split spreader with another spreader thatis not split without departing from the spirit and scope of theinvention. If both spreaders are split as described above, additionallateral travel is possible compared to embodiments having only onespreader that is split.

As shown in FIGS. 10 and 11, another embodiment of an instrument forspinal procedures, such as for treating spondylolisthesis, scoliosis,and the like, is a vertebral endplate spreader device 200 having avertebral endplate spreader 202 and a driver handle 204. Vertebralendplate spreader 202 includes a linkage 206 with a drive sprocket 208operatively connected for rotation relative to linkage 206 and with asecondary sprocket 210. Secondary sprocket 210 is operatively connectedfor rotation relative to linkage 206. Vertebral endplate spreader 202includes a belt 212 operatively connected to drive sprocket 208 andsecondary sprocket 210 to be driven about a belt axis B. Driver handle204 has a distal end 214 and a proximal end 216. Distal end 214 isoperatively connected to drive sprocket 208 to actuate rotation of belt212.

With reference now to FIG. 12, another embodiment of a vertebralendplate spreader 302 includes a gear transmission 322 operativelyconnected between drive sprocket 308 and distal end 314 of driver handle304 to reduce the required torque input through driver handle 304,making the rotation of drive sprocket 308 easier for the user.

As shown in FIGS. 13 and 14, drive sprocket 208 and secondary sprocket210 have different diameters to facilitate distraction betweenrespective endplates of two vertebrae 218 a and 218 b. For example,diameter of drive sprocket 208 can be larger than the diameter ofsecondary sprocket 210. The smaller diameter of secondary sprocket 210permits easier and less traumatic placement of spreader 202, while thelarger diameter of drive sprocket 208 facilitates distraction as belt212 is rotated.

With continued reference to FIGS. 13 and 14, correcting vertebralalignment includes engaging a top surface 224 of belt 212 to a firstvertebra 218 a, and engaging a bottom surface 226 of belt 212 ofvertebral endplate spreader 202 to a second vertebra 218 b proximate tofirst vertebra 218 a. First and second vertebrae, 218 a and 218 b,respectively, are separated by a distance L in a listhetic position.While vertebral endplate spreader 202 engages top and bottom surfaces224 and 226, respectively, of belt 212 with vertebrae 218 a and 218 bfrom a lateral approach, those skilled in the art will readilyappreciate that device 200 can be used to insert vertebral endplatespreader 202 from a posterior or anterior direction.

Now with reference to FIG. 15, belt 212 includes an outer texturedsurface 220 to engage respective endplates 219 a and 219 b of vertebrae218 a and 218 b for distraction and correction of vertebral alignment.Outer textured surface 220 includes teeth 222 pointed in acounter-clockwise direction with respect to a side of drive sprocket 208from which driver handle 204 extends. Those skilled in the art willreadily appreciate that teeth 222 can be pointed clockwise and/or can beneutral, e.g. neither clockwise nor counter-clockwise.

With continued reference to FIG. 15, rotating drive sprocket 208 rotatesbelt 212, as indicated schematically by the counter-clockwise arrows.Rotation of belt 212 moves top and bottom surfaces 224 and 226,respectively, of belt 212 in opposite directions from one anotherdistracting first and second vertebrae 218 a and 218 b, respectively,from one another and translating vertebrae 218 a and 218 b anteriorlyand posteriorly for correction of alignment. Those skilled in the artwill readily appreciate that translating includes moving the superior ofthe two vertebrae, e.g. vertebra 218 a, in a posterior direction tocorrect a listhesis condition of the vertebrae, and/or includes movingthe superior of the two vertebrae in an anterior direction to correct aretrolisthesis condition of the vertebrae. It is also contemplated thattranslating includes moving the two vertebrae relative to one another ina lateral direction to correct a lateral slippage condition of thevertebrae related to scoliosis. This translation in a lateral directioncan be achieved by inserting vertebral endplate spreader 202 from ananterior direction or a posterior direction, e.g. ninety degrees fromwhere vertebral endplate spreader 202 is shown in FIGS. 13-15, so thatwhen rotating drive sprocket 208 rotates belt 212 vertebrae 218 a and218 b are translated laterally with respect to one another.

As shown in FIGS. 16-18, after translation, vertebrae 218 a and 218 bare aligned with one another in the posterior to anterior direction. Itis contemplated that each vertebra 218 a and 218 b moves approximately½L in opposing directions in order to align with another. Once vertebrae218 a and 218 b aligned, an implant 228 a is inserted between vertebrae218 a and 218 b. After insertion of implant 228 a, a second implant 228b is inserted. Implant 228 b is similar to implant 228 a. Each implant228 a and 228 b includes bores 230 therethrough. Each bore 230 has abore entrance 232 defined along a first axis C and a bore exit 234defining a second axis D that is angled with respect to first axis C tofacilitate implantation of implants 228 a and 228 b. Implants 228 a and228 b are secured to the respective endplates 219 a and 219 b ofvertebrae 218 a and 218 b with flexible screws 236. Flexible screws 236pass into their respective bore 230 along first axis C and out of theirrespective bore 230 along second axis D. Once both implants 228 a and228 b are inserted and secured, vertebral endplate spreader 202 isremoved from the same direction as it was inserted, as indicatedschematically by the arrow in FIG. 18.

With reference now to FIGS. 19-20, another embodiment of a vertebralendplate spreader device 400 is shown. Device 400 is similar to device200. Device 400 includes a vertebral endplate spreader 402 and a driverhandle 404. Vertebral endplate spreader 402 includes a worm gear 407 fordriving drive sprocket 408 instead of a direct-drive drive sprocket,e.g. drive sprocket 208. Device 400 includes a worm shaft 409operatively connected to drive sprocket 408 through worm gear 407 torotate drive sprocket 408 when driven by the worm shaft 409. Worm shaft409 is shown as portion of a distal end 414 of driver handle 404,however, those skilled in the art will readily appreciate that wormshaft 409 can be separate from, but operatively connected to, driverhandle 404.

As shown in FIG. 21, drive sprocket 408 and secondary sprocket 410 aresimilar to drive sprocket 208 and secondary sprocket 210. Correctingvertebral alignment includes engaging a top surface 424 of a belt 412 ofvertebral endplate spreader 402 to a first vertebra 418 a, and engaginga bottom surface 426 of belt 412 to a second vertebra 418 b proximate tofirst vertebra 418 a. Belt 412 includes teeth 422, similar to teeth 422.While vertebral endplate spreader 402 engages top and bottom surfaces424 and 426, respectively, of belt 412 with vertebrae 418 a and 418 bfrom an anterior approach, those skilled in the art will readilyappreciate that device 400 can be used to insert vertebral endplatespreader 402 from a posterior and/or lateral direction.

With reference to FIGS. 20-21, once engaged, drive sprocket 408 isdriven by rotation of worm shaft 409 through driver handle 404. Drivesprocket 408 dives belt and secondary sprocket 410 similar to drivesprocket 208. Rotation of belt 412 moves top and bottom surfaces 424 and426, respectively, of belt 412 in opposite directions from one anotherdistracting first and second vertebrae 418 a and 418 b, respectively,from one another and translating vertebrae 418 a and 418 b anteriorlyand posteriorly for correction of alignment. It is also contemplatedthat vertebrae 418 a and 418 b can be translated in a lateral directionby inserting vertebral endplate spreader 402 from a lateral direction,so that when rotating drive sprocket 408 rotates belt 412 vertebrae 418a and 418 b are translated laterally with respect to one another.

As shown in FIGS. 22-23, after posterior-anterior translation, vertebrae418 a and 418 b are aligned with one another. Once vertebrae 418 a and418 b aligned, an implant 428 a is inserted between vertebrae 418 a and418 b. Implant 428 a is similar to implant 228 a. After insertion ofimplant 428 a, a second implant 428 b is inserted. Implant 428 b issimilar to implant 428 a. Once both implants 428 a and 428 b areinserted and secured, vertebral endplate spreader 402 is removed fromthe same direction as it was inserted, as indicated schematically by thearrow in FIG. 23.

With reference now to FIG. 24, a kit 500 for performing spinaldistraction and vertebral alignment includes a vertebral endplatespreader 502, similar to vertebral endplate spreaders 202 and 402, adriver handle 504, similar to driver handles 204 and 404 and a pluralityof implants 528 of varying sizes, similar to implants 228 a, 228 b, 428a and 428 b. Kit 500 includes additional vertebral endplate spreaders502 and additional driver handles 504 of varying sizes. Those skilled inthe art will readily appreciate that driver handles 504 can also beadjustable in length. Kit 500 also includes bendable screws 536, similarto screws 236 and 436, of varying sizes for use in one or more ofimplants 528.

While described above in the exemplary context of spondylolisthesis, itis contemplated that other conditions can also be treated using thesystems and methods of the invention. For example, there are severalforms of scoliosis. These include congenital, idiopathic, anddegenerative forms. Deformity of the spine involves a lateral or coronalcurvature of the spine. In the lumbar spine, especially in degenerativescoliosis, there is often a lateral slippage of one vertebra relative toanother. The instrumentation described above to reduce an anteriorspondylolisthesis can be used in a lateral approach on the convexity ofthe curve to reduce the scoliosis and at the same time allowintervertebral distraction. An instrument adapted from instruments 100,200 or 400 for treating scoliosis or similar applications can be of asmaller diameter and, in the case of instrument 100, can have one prongon each of the spreaders instead of the two prongs 150 shown anddescribed above.

The methods and instruments described herein advantageously allow forboth distraction and relative lateral repositioning of vertebrae.Additional advantages include allowing for disc space distraction whichenhances foraminal height. This increased foraminal height reduces thepotential for nerve root entrapment during a reduction of the listhesis.

The methods and systems of the present invention, as described above andshown in the drawings, provide for methods and instruments forcorrecting misalignment of vertebrae with superior properties includingdistracting and laterally repositioning vertebrae with the sameinstrument. While the apparatus and methods of the subject inventionhave been shown and described with reference to preferred embodiments,those skilled in the art will readily appreciate that changes and/ormodifications may be made thereto without departing from the spirit andscope of the subject invention.

What is claimed is:
 1. A vertebral endplate spreader for a vertebraldistraction instrument comprising: a proximal spreader sectionconfigured to be mounted to an end member of a distraction mechanism;and a distal spreader section operatively connected to the proximalspreader section for lateral movement relative to the proximal spreadersection, wherein the distal spreader section is configured and adaptedto engage a vertebra.
 2. A vertebral endplate spreader as recited inclaim 1, further comprising a pair of guides engaged with the proximaland distal spreader sections to maintain a parallel relationship betweenthe proximal and distal spreader sections during relative lateral travelof the proximal and distal spreader sections.
 3. A vertebral endplatespreader as recited in claim 2, wherein the guides are mounted to thedistal spreader section and are slideably engaged to the proximalspreader section.
 4. A vertebral endplate spreader as recited in claim1, further comprising a linear actuator engaged with the proximal anddistal spreader sections to actuate relative lateral travel of theproximal and distal spreader sections.
 5. A vertebral endplate spreaderas recited in claim 4, wherein the linear actuator includes a threadedscrew engaged to threads in the proximal spreader section, and rotatablyengaged with the distal spreader section so rotation of the threadedscrew adjusts separation of the proximal and distal spreader sectionsfor relative lateral travel thereof.
 6. A vertebral endplate spreader asrecited in claim 1, wherein at least one of the proximal and distalspreader sections includes a bone screw passage for accommodating a bonescrew to engage the distal spreader section to a vertebra.
 7. Avertebral endplate spreader as recited in claim 1, wherein the distalspreader section includes at least one tong for engaging a vertebralendplate.
 8. A method of correcting vertebral alignment comprising:engaging a distal spreader section of a first vertebral endplatespreader to a first vertebra; engaging a second vertebral endplatespreader to a second vertebra proximate to the first vertebra;distracting the first and second spreaders apart along a distractionaxis to distract the first and second vertebrae from one another; andtranslating the distal spreader section of the first spreader relativeto the second spreader laterally relative to the distraction axis forcorrection of alignment of the first and second vertebrae.
 9. A methodas recited in claim 8, wherein the steps of engaging the first andsecond spreaders to the vertebrae include approaching the vertebrae withthe spreaders from an anterior approach.
 10. A method as recited inclaim 9, wherein the step of translating includes moving the superior ofthe two vertebrae in a posterior direction to correct a listhesiscondition of the vertebrae.
 11. A method as recited in claim 8, whereinthe step of translating includes moving the superior of the twovertebrae in an anterior direction to correct a retrolisthesis conditionof the vertebrae.
 12. A method as recited in claim 8, wherein the stepsof engaging the first and second spreaders to the vertebrae includeapproaching the vertebrae with the spreaders from a lateral approach.13. A method as recited in claim 12, wherein the step of translatingincludes moving the two vertebrae relative to one another in a lateraldirection to correct a lateral slippage condition of the vertebraerelated to scoliosis.